Overvoltage protection

ABSTRACT

An embodiment of the present disclosure relates to an electronic circuit including a first switch coupling a first node of the circuit to an input/output terminal of the circuit; a second switch coupling the first node to a second node of application of a fixed potential; and a high-pass filter having an input coupled to the terminal and an output coupled to a control terminal of the second switch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of French Application No. 2000762,filed on Jan. 27, 2020, which application is hereby incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure generally relates to electronic devices andmethods, and in particular electronics circuits such as integratedcircuits and associated methods.

BACKGROUND

An electronic circuit typically has input/output terminals, intended toconnect the electronic circuit to other electronic circuits.

SUMMARY

There is a need to protect an electronic circuit against overvoltagesoccurring on terminals of the circuit.

There is a need to both test the operation of analog portions of anelectronic circuit and to protect the circuit against overvoltages.

An embodiment overcomes all or part of the disadvantages of knownelectronic circuits comprising an overvoltage protection device.

An embodiment overcomes all or part of the disadvantages of knownovervoltage protection methods.

An embodiment provides an electronic circuit, comprising a first switchcoupling a first node of the circuit to an input/output terminal of thecircuit; a second switch coupling the first node to a second node ofapplication of a fixed potential; and a high-pass filter having an inputcoupled to the terminal and an output coupled to a control terminal ofthe second switch.

According to an embodiment, the input of the high-pass filter is coupledto the input/output terminal by a diode, the diode preferably having itsanode facing the input/output terminal.

According to an embodiment, the input of the high-pass filter is coupledto another input/output terminal; and, preferably, the otherinput/output terminal is coupled to the second node by a circuit ofprotection against electrostatic discharges, more preferably a componenthaving a Zener diode function.

According to an embodiment, the high-pass filter has a cutoff frequencycapable of setting the second switch to the on state for at least onetime period modeled according to an overvoltage model, the time periodbeing preferably an electrostatic discharge period modeled according toa human body model.

According to an embodiment, the circuit further comprises at least onethird switch coupling at least a third node of the circuit to theinput/output terminal; and, preferably, at least one fourth switchcoupling the at least one third node to the second node, the output ofthe high-pass filter being further coupled to at least one controlterminal of the at least one fourth switch.

According to an embodiment, the circuit comprises a control circuitcoupled to control terminals of the first switch and of the at least onethird switch, configured so that the first switch and the at least onethird switch form branches of a multiplexer together.

According to an embodiment, the circuit further comprises an additionalswitch coupling the second node to the input/output terminal, the outputof the high-pass filter being coupled to a control terminal of theadditional switch.

According to an embodiment, the circuit further comprises a diodecoupling the second node to the input/output terminal and preferablyhaving its cathode facing the input/output terminal.

According to an embodiment, the circuit comprises a first transistorhaving a conduction terminal coupled to the second node, and a controlterminal or another conduction terminal coupled to the first node; and,preferably, at least one second transistor having a gate thicknessgreater than a gate thickness of the first transistor.

According to an embodiment, the first switch comprises a two-way passgate.

According to an embodiment, the first node is a node of application ofan analog signal.

According to an embodiment, the high-pass filter is passive.

An embodiment provides a method of protecting a circuit such as definedhereabove.

According to an embodiment, the method comprises the reception of theovervoltage by the high-pass filter, the reception causing the settingto the on state of the second switch, preferably in the absence of apower supply voltage of the circuit.

An embodiment provides a method of testing a circuit such as definedhereabove, the method preferably comprising the application and/or thereception of a signal on the input/output terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will bedescribed in detail in the following description of specific embodimentsgiven by way of illustration and not limitation with reference to theaccompanying drawings, in which:

FIG. 1 partially and schematically shows an embodiment of an electroniccircuit;

FIG. 2 schematically shows an example of a high-pass filter of theelectronic circuit of FIG. 1 ;

FIG. 3 schematically shows an example of a switch of the electroniccircuit of FIG. 1 ; and

FIG. 4 schematically shows another embodiment of an electronic circuit.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Like features have been designated by like references in the variousfigures. In particular, the structural and/or functional features thatare common among the various embodiments may have the same referencesand may dispose identical structural, dimensional and materialproperties.

For the sake of clarity, only the operations and elements that areuseful for an understanding of the embodiments described herein havebeen illustrated and described in detail. In particular, portions ofelectronic circuits are not described in detail, the describedembodiments being compatible with such usual portions of electroniccircuits.

Unless indicated otherwise, when reference is made to two elementsconnected together, this signifies a direct connection without anyintermediate elements other than conductors, and when reference is madeto two elements coupled together, this signifies that these two elementscan be connected or they can be coupled via one or more other elements.

In the following description, when reference is made to terms qualifyingabsolute positions, such as terms “front”, “rear”, “top”, “bottom”,“left”, “right”, etc., or relative positions, such as terms “above”,“under”, “upper”, “lower”, etc., or to terms qualifying directions, suchas terms “horizontal”, “vertical”, etc., it is referred to theorientation of the drawings or to a . . . in a normal position of use.

Unless specified otherwise, the expressions “around”, “approximately”,“substantially” and “in the order of” signify within 10%, and preferablywithin 5%.

Unless specified otherwise, ordinal numerals such as “first”, “second”,etc. are only used to distinguish elements from one another. Inparticular, these adjectives do not limit the described devices andmethods to a specific order of these elements.

FIG. 1 partially and schematically shows an embodiment of an electroniccircuit 100. Electronic circuit 100 has an input/output terminal 110and, preferably, other input/output terminals, not shown.

Electronic circuit 100 may comprise one or a plurality of electronicchips. Such a chip is defined by a substrate such as a semiconductorwafer portion and electronic circuits located inside of and on thesubstrate. Circuit 100 may be formed by an electronic chip. In thiscase, the input/output terminals of circuit 100 are defined by theconductive connection tracks located on the chip.

The electronic chip(s) may be located in one or a plurality ofintegrated circuits. Thus, electronic circuit 100 may comprise or beformed by an integrated circuit. The term integrated circuit designatesthe assembly of a package and of one or a plurality of chips located inthe package. The package comprises electrically-conductive connectionareas located at the surface of the package or electrically-conductivepins coming out of the package. In the case where electronic circuit 100is an integrated circuit, the input/output terminals of circuit 100 maybe defined by the connection pins or areas of the package.

As an example, electronic circuit 100 is a time-of-flight ToFmeasurement circuit, or an image sensor or, for example, a circuitdedicated to delivering power supply voltages.

Electronic circuit 100 comprises a portion 120 and a device 130 couplinginput/output terminal 110 to the portion 120 of circuit 100. Portion 120carries out one of or a plurality of the usual functions of anelectronic circuit, such as, for example, the generation of one or aplurality of DC voltages, the generation of an oscillating signal,and/or, still as an example, functions of analog-to-digital and/ordigital-to-analog conversion. For this purpose, portion 120 typicallycomprises one or a plurality of transistors 122.

In an example of transistor 122, the transistor has a control terminal124 (that is, in the case of a field-effect transistor, a gate terminal)coupled, preferably connected, to device 130. Transistor 122 hasconduction terminals 126 and 128. The term conduction terminals of atransistor or of a switch designates terminals of the transistor or ofthe switch that the transistor or switch electrically connects togetherin a conductive state and isolates from each other in a non-conductivestate. In the shown example, conduction terminal 126, typically a drainterminal, is coupled to elements, not shown, of the portion 120 ofcircuit 100.

Preferably, transistor 122 has one of its conduction terminals (terminal128 in the shown example), typically a source terminal, coupled, morepreferably connected, to a node of application of a fixed potential GND.Node GND is preferably formed by the ground. The fixed potential then isthe ground potential, and this potential is used as a reference. NodeGND may, as a variation, be formed by any node or terminal, for example,an input/output terminal, with a potential having a constant intervalrelative to the ground potential. Such a potential may then beregulated, for example, supplied by a power supply.

Circuit 100 further comprises a node 140 coupled, for example, by aswitch 142, to the portion 120 of circuit 100. Switch 142 may compriseone or a plurality of transistors in series. Switch 142 may be omitted,and node 140 is then preferably connected to portion 120.

Node 140 is a node of application of a signal originating from and/orsent to portion 120. In the shown example, node 140 is coupled (byoptional switch 142) to the gate of transistor 122 and, thereby, thesignal applied to node 140 is sent to portion 120. In another example,not shown in FIG. 1 , node 140 is coupled, for example by a switch, oris connected, to conduction terminal 126, and control terminal 124 iscoupled to other elements of portion 120 of circuit 100. In this otherexample, the signal applied to node 140 then originates from portion120. In normal operation, that is, in operation and in the absence of anovervoltage, the voltage between nodes 140 and GND is located within arange. As an example, for this voltage, the normal operating rangeextends from 0 to 4.0 V, preferably from 0 to 1.7 V.

Preferably, the signal applied to node 140 has a positive potential,that is, greater than that of node GND. Transistor 122 is then morepreferably of N-channel type. This is not limiting, and the signs of thepotential differences, that is, of the voltages, may be exchanged in thedescribed embodiments, preferably by also exchanging the N and Pconductivity types of the semiconductors, for example, by exchanging thechannel types of the field-effect transistors and the directions of thepossible diodes.

Device 130 comprises a first switch 150. Switch 150 couples input/outputterminal no to node 140. More particularly, switch 150 has a conductionterminal 152 coupled, preferably connected, to node 140, and aconduction terminal 154 coupled, preferably connected, to input/outputterminal no. Switch 150 has a control terminal 156 coupled to elements,not shown, of electronic circuit 100. An example of switch 150 isdescribed hereafter in relation with FIG. 3 .

In operation, first switch 150 has the function, when it is set to theconductive state, of applying to input/output terminal 110 a signaloriginating from the portion 120 of circuit 100 and/or of applying toportion 120 a signal applied to input/output terminal 110 by a deviceexternal to electronic circuit 100. When it is in the off state, switch150 isolates input/output terminal 110 and node 140 from each other.

Preferably, first switch 150 is set to the on state for at least part ofa phase of testing of electronic circuit 100, and in particular oftesting of portion 120. For this purpose, a test device external tocircuit 100 is used. The test device applies signals to input/outputterminal 100 and/or receives signals applied by switch 150 toinput/output terminal 110. It is then determined, from the signalsoriginating from input/output terminal 110, whether the operation ofportion 120 corresponds to an expected operation. Any usual method oftesting a portion of an electronic circuit such as portion 120 may beimplemented. The test is for example performed in factory. Circuit 100then typically is a circuit randomly selected from amongsimultaneously-manufactured circuits, which are identical (to withinmanufacturing tolerances). Preferably, switch 150 is left in the offstate outside of the test phase.

Device 130 further comprises a second switch 160. Switch 160 couplesnodes 140 and GND together. More particularly, a conduction terminal 162of switch 160 is coupled, preferably connected, to the node 140 ofapplication of a signal sent to and/or originating from the portion 120of circuit 100. Another conduction terminal 164 of switch 160 iscoupled, preferably connected, to node GND. Preferably, switch 160comprises or is formed by an N-channel field effect transistor. Terminal162 then is a drain terminal of the transistor, and terminal 164 then isa source terminal of the transistor.

Device 130 further comprises a high-pass filter 170 (HPF) having aninput 172 coupled, preferably by a diode 195, to input/output terminal110 and an output 174 coupled to the control terminal of second switch160. The anode of diode 195 preferably faces terminal no. In avariation, diode 195 is omitted, the input of high-pass filter 170 beingfor example connected to input/output terminal 110.

Preferably, high-pass filter 170 is referenced with respect to apotential applied to a node 176. The potential of node 176 is apotential for turning second switch 160 to the off state. In otherwords, the application of the potential of node 176 to the controlterminal of switch 160 causes the setting of switch 160 to the off state(non-conductive state). For this purpose, preferably, node 176 isconnected to node GND.

High-pass filter 170 is provided so that, when the potential applied toinput 172 is constant with respect to the potential of node 176,high-pass filter 170 applies the potential of node 176 to the controlterminal of second switch 160. An example of high-pass filter 170 isdescribed hereafter in relation with FIG. 2 .

An overvoltage may occur between input/output terminal 110 and node GND.The voltage between input/output terminal 110 and node GND then tends tocome out of the normal operating range defined hereabove.

An embodiment concerns an overvoltage originating from an electrostaticdischarge when the circuit is not operating. Preferably, the concernedovervoltage is positive, in other words, the voltage between terminals110 and node GND tends to rise above an upper limit of the normaloperating range of this voltage. In this case, more preferably, secondswitch 160 comprises, or is formed by an N-channel field-effecttransistor.

The electrostatic discharge typically originates from a handling by aperson when electronic circuit 100 is not connected, for example, whencircuit 100 is packed or unpacked before the installation and theconnection of circuit 100 in an electronic device. In an example of thisembodiment, the electrostatic discharge is modeled according to a usualmodel of electrostatic discharge from the human body. The human bodymodel may comprise a charged capacitive element and a dischargeresistor. As an example, the electrostatic discharge has a modeledduration in the range from 1 μs to 5 μs.

The electrostatic discharge is received by high-pass filter 170,preferably after having crossed diode 195. According to an example, itis provided for high-pass filter 170 to have a cutoff time, defined bythe inverse of a −3 dB cutoff frequency, greater than the modeledduration. The cutoff time is then greater than 1 μs, preferably greaterthan 2 μs. As a result, after the reception of the discharge byhigh-pass filter 170, switch 160 is set to the on state for at least theduration of the electrostatic discharge. This example is not limiting,and high-pass filter 170 may have any cutoff frequency capable ofsetting the second switch to the on state for at least the modeledduration. Based on the above example, it will be within the abilities ofthose skilled in the art to determine such a cutoff frequency, accordingto the type of the selected filter and to the electrostatic dischargemodel, for example, by implementing a model of this type of filter andthe discharge model for various cutoff frequency values.

As a result, even if switch 150 is in the on state and the electrostaticdischarge reaches node 140, the discharge is carried off to node GND.Thereby, it is avoided for the electrostatic discharge to cause adeterioration of transistor 122 such as a gate insulator breakdown. Inthe shown example, in the absence of a carrying off of the discharge,the breakdown would risk being caused by a gate-source voltage higherthan a breakdown voltage of the gate insulator of transistor 122. Thus,due to the fact that the discharges are carried off, device 130 protectsportion 120 against electrostatic discharges arriving into circuit 100through input/output terminal 110.

According to the embodiments where electronic circuit 100 comprisesdiode 195, electronic circuit 100 further comprises, preferably, aninput/output terminal 190. Diode 195 couples input/output terminals 110and 190 to each other. The cathode of the diode preferably facesinput/output terminal 190. The input 172 of high-pass filter 170 iscoupled, preferably connected, to input/output terminal 190.

Input/output terminal 190 may be a supply terminal of the portion 120 ofcircuit 100. In operation, in the absence of an overvoltage, the powersupply voltage (that is, the potential difference between terminal 190and node GND) is used by transistor 120. The power supply voltage ispreferably substantially constant, so that the high-pass filter does notcause the setting to the on state of switch 160. Indeed, such a settingto the on state would risk disturbing the operation of circuit 100.

In operation, input/output terminal 110 is preferably left floating (inother words, only used during the test phase) or is held at a potentiallower than that of input/output terminal 190. Diode 195 is thennon-conductive.

In test phase, input/output terminal 190 is preferably held at apotential greater than that of input/output terminal 110. As a result,diode 195 remains in the non-conductive state during the test. Thisenables to apply and/or to receive, on input/output terminal 110,signals having a frequency and/or an amplitude sufficient for there tobe, in the absence of non-conductive diode 195, a risk for the high-passfilter to turn switch 160 on after the reception of the signals. Indeed,such a setting to the on state would risk disturbing the testing ofcircuit 100.

Examples of an embodiment concerning positive electrostatic dischargeshave been described hereabove. Another embodiment concerning negativeelectrostatic discharges differs from the above embodiment in that thesecond switch 160 is preferably a P-channel field-effect transistor.Further, the describe embodiments are not limited to the cases ofovervoltages originating from electrostatic discharges from a person.Thus, although the above-described modeled duration is provided by amodel of an electrostatic discharge originating from the human body, anyovervoltage model may be used to define the modeled duration. High-passfilter 170 then receives the overvoltage, which causes the setting tothe high state of switch 160. The cutoff frequency selected forhigh-pass filter 170 is then capable of setting the second switch to theon state for at least the modeled duration, which enables to protectcircuit 100 against the overvoltage.

FIG. 2 schematically shows an example of the high-pass filter 170 of theelectronic circuit 100 of FIG. 1 .

According to this example, high-pass filter 170 is of resistor-capacitortype RC, that is, high-pass filter 170 comprises a capacitive element210, preferably a capacitor, coupling input 172 to the output 174 ofhigh-pass filter 170, and a resistor 220 coupling the output 174 ofhigh-pass filter 170, and a resistor 220 coupling the output 174 ofhigh-pass filter 170 to node 176. The shown example is not limiting andhigh-pass filter 170 may be of any type.

Preferably, as in the shown example, high-pass filter 170 is passive,that is, the power supplied by high-pass filter 170 to control switch160 is formed by all or part of the power received by passive high-passfilter 170 on its input 172. In other words, high-pass filter 170receives, outside of input 172 and of node 176, power from no othernode. In particular, high-pass filter 170 does not receive power from apower supply node. Preferably, part of the power received on input 172is dissipated in high-pass filter 170, here in resistor 220. High-passfilter 170 may be of any passive type. However, the shown example hasthe advantage of being simpler than other types of passive filters.

In the absence of a connection of electronic circuit 100 to a powersupply, typically in the cases described hereabove of handling ofcircuit 100 by a person, the control terminal of switch 150 may befloating. When an overvoltage occurs, the on/off state of switch 150 isnot fixed, and switch 150 might for example be on. Due to the fact thathigh-pass filter 170 is passive, high-pass filter 170 sets second switch160 to the on state during the discharge, including in the absence of apower supply voltage. Thus, the fact of providing for high-pass filter170 to be passive enables to protect circuit 100 against overvoltageseven when circuit 100 is not powered.

FIG. 3 schematically shows an example of the first switch 150 of theelectronic circuit 100 of FIG. 1 .

According to this example, first switch 150 is a two-way pass gate.Preferably, first switch 150 then comprises an N-channel field effecttransistor 310 and a P-channel field-effect transistor 320 electricallyin parallel between the conduction terminals 152 and 154 of switch iso.The source of each of transistors 310 and 320 is coupled, preferablyconnected, to the drain of the other one of transistors 310 and 320. Thegates of transistors 310 and 312 are coupled to each other by aninverter 158. The input of inverter 158 forms the control terminal 156of switch 150. As an example, the control terminals of transistors 310and 320 are coupled, preferably connected, respectively to the input andthe output of inverter 158. This example is not limiting, and switch 150may be any switch, preferably capable of being included in integratedcircuit 100, more preferably forming a two-way pass gate.

When switch 150 is in the on state and in particular during the testphase, the signals originating from input/output terminal 110 andapplied to node 140 by two-way pass gate 150 may be analog. The signalsapplied by the portion 120 of circuit 100 to node 140 and, by pass gate150, to input/output terminal no, may also be analog. In other words,node 140 then is a node of application of an analog signal. Analogsignal means a signal conveying information varying continuously when avalue of the signal, such as a voltage, varies continuously.

For this purpose, as an example, the portion 120 of circuit 100comprises one or a plurality of analog circuits coupled, preferablyconnected, to node 140. In other words, transistor 122 is, in thisexample, located in an analog circuit. Call analog circuit a circuitconfigured to receive, use, or deliver an analog signal. As an example,the analog circuit is a portion of a digital-to-analog oranalog-to-digital converter, or also, for example, all or part of aregulated voltage supply circuit.

Thus, when pass gate 150 is conductive, in particular during the testphase, the analog signal sent to or originating from portion 120 isapplied to input/output terminal 110 by an external device or by passgate 150.

FIG. 4 schematically shows another embodiment of an electronic circuit400. Circuit 400 comprises elements identical or similar to those of theelectronic circuit 100 of FIG. 1 , arranged identically or similarly.These elements are not described again in detail. Only the differencesbetween circuit 400 and the circuit 100 of FIG. 1 are highlighted.Similarly, circuit 400 implements operating and test steps identical orsimilar to those of the circuit 100 of FIG. 1 . These steps are notdescribed in detail again either. Only the differences between themethods implemented by circuit 400 and the circuit 100 of FIG. 1 arehighlighted.

According to an embodiment, electronic circuit 400 comprises, inaddition to node 140, one or a plurality of nodes 140-i (140-1, 140-2),i being an index varying from 1 to the number of nodes 140-i. Each ofnodes 140-i is coupled, preferably connected, to the portion 120 ofcircuit 400.

The portion 120 of circuit 400 then comprises, in addition to transistor122, one or a plurality of transistors 122-j (122-1) coupled, preferablyconnected, to nodes 140-i, j being an index varying between 1 and thenumber of transistors 122-j coupled or connected to node 140-i. In theshown example, transistor 122-1 has a source terminal coupled,preferably connected, to node GND, a drain terminal coupled, preferablyconnected, to node 140-1, and a control terminal coupled, preferablyconnected, to elements, not shown, of portion 120.

Electronic circuit 400 also comprises, in addition to switch 150, one ora plurality of switches 150-i coupling the respective nodes 140-i toinput/output terminal 110. In other words, for each of nodes 140-i,switch 150-i has a conduction terminal coupled, preferably connected, tonode 140-i, and another conduction terminal coupled, preferablyconnected, to input/output terminal 110. Preferably, each of switches150-i comprises, or is formed by, a two-way pass gate such as that ofFIG. 3 .

Preferably, electronic circuit 400 comprises, in addition to switch 160,one or a plurality of switches 160-i coupling the respective nodes 140-ito node GND. In other words, for each of nodes 140-i, switch 160-i has aconduction terminal coupled, preferably connected, to node 140-i, andanother conduction terminal coupled, preferably connected, to node GND.Preferably, switches 160-i are all controlled by high-pass filter 170.As a variation, a plurality of high-pass filters having their inputscoupled, or connected, to input/output terminal 110, and each having anoutput controlling one or a plurality of switches 160-i, may beprovided.

In case of a positive overvoltage between input/output terminal 110 andnode GND, the operation of switches 150-i and 160-i is the same as that,described in relation with FIG. 1 , of respective switches 150 and 160.As a result, in addition to transistor 122, transistors 122-j are alsoprotected against overvoltages. In the shown example, transistor 122-1is protected against a breakdown of the gate insulator caused by avoltage greater than a breakdown voltage between the drain and the gateof transistor 122-1.

According to an embodiment, circuit 400 further comprises a switch 460coupling input/output terminal 110 to node GND. The output 174 ofhigh-pass filter 170 is then coupled to a control terminal of switch460. In case of an overvoltage between input/output terminal 110 andnode GND, this overvoltage is at least partly discharged before reachingswitches 150, 150-i. This results in an improvement of the protectionwith respect to embodiments where switch 460 is not provided. Further,this may enable to protect switches 150, 150-i against the overvoltage,or to improve the protection of the switches.

According to an embodiment, circuit 400 comprises a diode 412 couplinginput/output terminal 110 to node GND. In the case where the normaloperating range of the voltage between input/output terminal 110 andnode GND is entirely positive, diode 412 has its cathode facinginput/output terminal 110. Thus, if a negative overvoltage occurs, thatis, an overvoltage during which the voltage between input/outputterminal 110 and node GND tends to become negative (potential ofterminal 110 smaller than that of node GND), this overvoltage isdischarged. This thus enables to protect the transistors 122, 122-j ofthe portion 120 of circuit 400 against negative overvoltages.

According to an embodiment, circuit 400 further comprises a controlcircuit 480 (CTRL) coupled, preferably connected, to the controlterminal 156 of switch iso. Control circuit 480 may further be coupled,preferably connected, to the control terminals 156-i (156-1, 156-2) ofthe respective switches 150-i. Preferably, control circuit 480 receivesa digital signal 482. Digital signal 482 is, more preferably, formed ofa plurality of bits. Control circuit 480 is configured to control theon/off state of switches 150, 150-i according to digital signal 482. Inother words, control circuit 480 is configured so that switches 150,150-i form, with control circuit 480, branches of a multiplexer 490.

Preferably, electronic circuit 400 is configured so that multiplexer 490connects switches 150, 150-i to input/output terminal 110, one by oneand/or in successive groups. In particular, during the test phase, theoperation of a plurality of transistors and/or elements and/or circuitsof portion 120 may be tested with the signal input/output terminal 110to apply/receive test signals. Such a test method is not described indetail, the described embodiments being compatible with usual methods oftesting portions of an electronic circuit.

According to an embodiment, the portion 120 of circuit 400 comprises, inaddition to transistor 122 and the possible transistors 122-j,transistors 422-k 1, k1 being an index varying between 1 and the numberof transistors 422-k 1.

Preferably, transistor 122 and transistors 122-j have a same relativelysmall gate thickness, for example, smaller than 2 nm, for example, equalto 1.7 nm. Transistor(s) 422-k 1 then typically have a same relativelylarge gate thickness, for example, greater than 3 nm, for example, equalto 5 nm. In other words, transistor(s) 422-k 1 have a gate thicknessgreater than that of transistor(s) 122, 122-j. In this case, preferably,the normal operating range, such as defined hereabove, of the voltagebetween the gate and the source or of the voltage between the drain andthe gate, is wider for transistor(s) 422-k 1 than for transistor(s) 122,122-j. As an example, this range extends from 0 to approximately 4 V fortransistor(s) 422-k 1, and from 0 to approximately 1.7 V fortransistor(s) 122, 122-j. More preferably, a voltage greater than athreshold of deterioration of transistors 122, 122-j, for example, thebreakdown voltage of the transistors, is located in the normal operatingrange of transistors 422-k 1.

Input/output terminal 190 may be a terminal of application of a powersupply voltage of a circuit of the portion 120 comprising transistors422-k 1. Input/output terminal 190 may also be an input or an output ofa signal originating from and/or sent to transistors 422-k 1. Portion120, comprising transistors 122, 122-j, and 422-k 1 having differentnormal operating voltage ranges, is not described in detail herein, thedescribed embodiments being compatible with such usual portions ofelectronic circuits.

In operation, in the absence of an overvoltage, the voltage applied toinput/output terminal 190 is used by transistors 422-k 1. For example,the voltage applied to input/output terminal 190 is a voltage greaterthan the threshold of deterioration of transistors 122, 122-i. In theshown example, input/output terminal 190 is coupled by a Zener diode 414to node GND. Zener diode 414 has its cathode facing input/outputterminal 190 in the preferred case where, in the absence of anovervoltage, the voltage between input/output terminal 190 and node GNDis positive (potential of input/output terminal 190 greater than that ofnode GND). The reverse threshold voltage of Zener diode 414 is providedto discharge an overvoltage towards node GND to protect transistors422-k 1 against an overvoltage. Zener diode 414 thus forms anovervoltage protection circuit. Zener diode 414 may be replaced with anycomponent having the function of a Zener diode, that is, conducting thecurrent when the voltage thereacross rises above a predefined threshold.More generally, the Zener diode may be replaced with any overvoltageprotection circuit. According to an advantage of a protection circuitsuch as Zener diode 414, switches 150 may be selected so that theprotection circuit protects switches 150 against the overvoltage,including in the case where switch 460 is omitted. The protectioncircuit may also, as a variation, be omitted.

Preferably, electronic circuit 400 further comprises one or a pluralityof switches 450-k 2 (450-1, 450-2), k2 being an index varying from 1 tothe number of switches 450-k 2. Switches 450-k 2 couple transistors422-k 1 to input/output terminal 110. More particularly, each switch450-k 2 has a conduction terminal coupled, preferably connected, toinput/output terminal 110, and another conduction terminal coupled,preferably connected, to one or a plurality of transistors 422-k 1. Inthe shown example, switch 450-1 is coupled, preferably connected, to agate terminal of transistor 422-1. In this example, switch 450-2 iscoupled, preferably connected, to a drain terminal of transistor 422-2.Each of transistors 422-k 1 may have a source terminal coupled orconnected to node GND.

Preferably, control circuit 480 is coupled, preferably connected, to oneor a plurality of the respective control terminals of switch(es) 450-k2. More preferably, control circuit 489 is configured so that switch(es)150, 150-i and switch(es) 450-k 2 form branches of multiplexer 490.Based on the same input/output terminal 110, both the functionalities ofportion 120 implemented by transistors 122, 122-j and by transistors422-k 1 can then be tested.

It could have been devised to discharge an overvoltage betweeninput/output terminal 110 and node GND when this overvoltage exceeds agiven threshold such as a threshold voltage of a reverse-biased Zenerdiode. However, due to the fact that the voltage applied in normaloperation to transistors 422-k 1 is greater than the threshold ofdeterioration of transistors 122, 122-j, it would have been difficult toselect the threshold voltage of the Zener diode to both: protecttransistors 122, 122-j; and be able to apply to input/output terminal190 a sufficiently high voltage to test the operation of transistors422-k 1 without discharging this voltage to node GND through the Zenerdiode.

As a comparison, the fact of providing to discharge the overvoltage bythe setting to the on state of switch(es) 160, 160-i, and of thepossible switch 460, through the high-pass filter 170 receiving theovervoltage, enables to test the functionalities of portion 120implemented by all transistors 122, 122-j, and 422-k 1 by using thesingle input/output terminal 110, and enables to protect transistors122, 122-j.

In case of an overvoltage between input/output terminal 110 and nodeGND, the operation is the same as that described hereabove. In case ofan overvoltage between input/output terminal 190 and node GND, high-passfilter 170 turns on switches 160, 160-i, and possibly switch 460 duringthe overvoltage.

A protection of transistors 122, 122-j against overvoltages reachinginput/output terminal 110 and against overvoltages reaching input/outputterminal 190 is thus obtained.

Various embodiments and variants have been described. Those skilled inthe art will understand that certain features of these embodiments canbe combined and other variants will readily occur to those skilled inthe art.

Finally, the practical implementation of the described embodiments andvariants is within the abilities of those skilled in the art based onthe functional indications given hereabove.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present invention. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting. The present invention is limited only as defined in thefollowing claims and the equivalents thereto.

What is claimed is:
 1. An electronic circuit comprising: a first switchcoupling a first node of the electronic circuit to a first input/outputterminal of the electronic circuit; a second switch coupling the firstnode to a second node of application of a fixed voltage potential; ahigh-pass filter having an input coupled to the first input/outputterminal and an output coupled to a control terminal of the secondswitch; and a second input/output terminal coupled to the input of thehigh-pass filter, and coupled to the second node by a circuit ofprotection against electrostatic discharges.
 2. The electronic circuitaccording to claim 1, wherein the input of the high-pass filter iscoupled to the first input/output terminal by a diode, the diode havingits anode facing the first input/output terminal.
 3. The electroniccircuit according to claim 1, wherein the high-pass filter has a cutofffrequency configured to set the second switch to an on-state for atleast one time period modeled according to an overvoltage model, thetime period being an electrostatic discharge period modeled according toa human body model.
 4. The electronic circuit according to claim 1,further comprising: at least one third switch coupling at least onethird node of the electronic circuit to the first input/output terminal;and at least one fourth switch coupling the at least one third node tothe second node, the output of the high-pass filter being furthercoupled to at least one control terminal of the at least one fourthswitch.
 5. The electronic circuit according to claim 4, comprising acontrol circuit coupled to control terminals of the first switch and ofthe at least one third switch, and configured so that the first switchand the at least one third switch form branches of a multiplexertogether.
 6. The electronic circuit according to claim 1, furthercomprising an additional switch coupling the second node to the firstinput/output terminal, the output of the high-pass filter being coupledto a control terminal of the additional switch.
 7. The electroniccircuit according to claim 1, further comprising a diode coupling thesecond node to the first input/output terminal and having its cathodefacing the first input/output terminal.
 8. The electronic circuitaccording to claim 1, comprising: a first transistor having a firstconduction terminal coupled to the second node, and a first controlterminal or a second conduction terminal coupled to the first node; andat least one second transistor having a first gate thickness greaterthan a second gate thickness of the first transistor.
 9. The electroniccircuit according to claim 1, wherein the first switch comprises atwo-way pass gate.
 10. The electronic circuit according to claim 1,wherein the first node is a node of application of an analog signal. 11.The electronic circuit according to claim 1, wherein the high-passfilter is passive.
 12. A method of protecting an electronic circuitagainst an overvoltage, the electronic circuit comprising a first switchcoupling a first node of the electronic circuit to a first input/outputterminal of the electronic circuit, a second switch coupling the firstnode to a second node of application of a fixed voltage potential, ahigh-pass filter having an input coupled to the first input/outputterminal and an output coupled to a control terminal of the secondswitch, and a second input/output terminal coupled to the input of thehigh-pass filter, and coupled to the second node by a circuit ofprotection against electrostatic discharges, the method comprising:receiving the overvoltage by the high-pass filter; setting, by thehigh-pass filter, the second switch to an on-state based on thereceiving the overvoltage; and providing a Zener diode function by thecircuit of protection against electrostatic discharges.
 13. The methodaccording to claim 12, further comprising an absence of a power supplyvoltage being applied to the electronic circuit during the receiving theovervoltage.
 14. The method according to claim 12, further comprisingthe high-pass filter operating passively.
 15. The method according toclaim 12, further comprising the high-pass filter setting the secondswitch to the on-state for at least one time period modeled according toan overvoltage model, the time period being an electrostatic dischargeperiod modeled according to a human body model.
 16. A method of testingan electronic circuit comprising a first switch coupling a first node ofthe electronic circuit to a first input/output terminal of theelectronic circuit, a second switch coupling the first node to a secondnode of application of a fixed voltage potential, a high-pass filterhaving an input coupled to the first input/output terminal and an outputcoupled to a control terminal of the second switch, and a secondinput/output terminal coupled to the input of the high-pass filter, andcoupled to the second node by a circuit of protection againstelectrostatic discharges, the method comprising: applying and/orreceiving a signal to and/or from, respectively, the first input/outputterminal; and providing a Zener diode function by the circuit ofprotection against electrostatic discharges.
 17. The method according toclaim 16, wherein the electronic circuit further comprises at least onethird switch coupled between the first node of the electronic circuitand the first input/output terminal, and the method further comprises:setting the third switch to an on-state during the testing to bypass thehigh-pass filter.
 18. The method according to claim 16, furthercomprising: holding the second input/output terminal at a first voltagepotential greater than a second voltage potential of the firstinput/output terminal.
 19. The method according to claim 18, wherein theapplying and/or receiving comprises applying and/or receiving signalshaving a frequency and/or an amplitude that would be sufficient for thehigh-pass filter to set the second switch to an on-state in an absenceof the first voltage potential.
 20. The electronic circuit of claim 1,wherein the circuit of protection against electrostatic discharges is aZener diode.